1. Field of the Invention
This invention relates generally to a process for dicing semiconductor wafers into individual units and more particularly to a process for dicing such wafers from the backside thereof so that contamination of the face of the unit by the dicing operation is avoided.
2. Description of the Prior Art
Many mechanical methods of structurally weakening semiconductor wafers such that they will fracture on predetermined planes are known to prior art. Such methods include sawing, sandblasting and scribing with a diamond point.
Additionally, U.S. Pat. No. 3,816,700 discusses laser scribing, i.e., cutting partially through a semiconductor wafer with a laser beam and applying mechanical stresses to the material to break it into individual dice. Such wafers have active devices or integrated circuits formed in their face or front surface.
When a laser beam is so directed at this front surface a trench or scribe work caused by evaporation of the wafer material is formed. The material evaporated from the trench resolidifies on the face of the body contaminating the circuits on the face of the body. Additionally, this resolidified material or slag can build upon each side of the body such that ridges of slag are formed which ridges are high enough to interfere with subsequent testing and bonding of the units in the wafer.
U.S. Pat. No. 3,824,678 teaches the dicing of beam lead circuits by evaporating away about 90 percent of the semiconductor wafer with a laser beam directed at the backside of the wafer.
This patent avoids the problem of contamination being deposited on the face of the wafer. However, because the wafer is not completely cut through it is necessary to break the uncut silicon and this breakage of the uncut silicon because of the crystallographic orientation of the silicon can cause cracks to propagate into the circuits created on the face of the semiconductor wafer. Also, such uneven breakage of the silicon leaves sharp shards extending from the edge of the dice which shards will interfere with subsequent handling of the units.
To overcome these disadvantages a dicing operation is preferred that will provide separate units from a semiconductor wafer while avoiding surface contamination and handling problems associated with the prior art. The present invention provides such dicing operation.